Lipophilicity and Steric Constraints Govern V-Shaped Inhibition of Human and Rat Placental 3β-Hydroxysteroid Dehydrogenase by Dialkyldimethylammonium Disinfectants: Implications for Progesterone Dysregulation.

Dialkyldimethylammonium chemicals (DDAs) are quaternary ammonium disinfectants. However, their effects on progesterone synthesis in placentas remain unclear. This study aims to study structure-activity relationship (SAR) and mechanism of DDAs (C2-C18) as inhibitors of human (3β-HSD1) and rat (3β-HSD4) placental 3β-hydroxysteroid dehydrogenase/Δ5-Δ4 isomerase (3β-HSD), a key enzyme in progesterone synthesis. DDAs exhibited a distinct V-shaped SAR to inhibit 3β-HSD, which was dependent on alkyl chain length. The inhibitory potency peaked with the C12 analogue, demonstrating the highest potency in human (IC50 = 4.78 μM) and rat (IC50 = 2.08 μM) assays. Conversely, a significant reduction in activity was observed with the C18 analogue, as evidenced by the substantially higher IC50 values (human: 19.1 μM; rat: 18.68 μM). Kinetic analyses confirmed mixed/noncompetitive mechanisms via NAD+/steroid interface binding, supported by molecular docking and 3D-QSAR pharmacophores highlighting hydrophobic interactions. Cellular assays in JAr cells demonstrated reduced progesterone secretion. Network toxicology analysis identifies human 3β-HSD1 as a central hub within a pathogenic network for recurrent spontaneous abortion, suggesting its dysregulation to disrupted progesterone metabolism and key signaling pathways. These findings propose DDAs as novel placental 3β-HSD inhibitors, with implications for endocrine-disrupting effects.